E3 PreliminaryPreliminaryPEM not requiredCase-ControlPeer-reviewedReviewed
Chronic fatigue syndrome and complement activation.
Geller, Robert Dennis, Giclas, Patricia C · BMJ case reports · 2009 · DOI
Quick Summary
This report follows one patient who developed ME/CFS after a severe Epstein-Barr virus infection. Standard medical tests came back normal, but when doctors tested for complement activation (part of the immune system's inflammatory response), they found it was abnormally active. The patient remained unwell for about 2 years while showing these signs of complement activation, then recovered.
Why It Matters
This study introduces complement activation as a potentially measurable biomarker in ME/CFS, offering a testable immune mechanism in patients with post-viral onset. It supports the biological basis of ME/CFS at a time when many conventional tests appear normal, validating the experience of patients with negative standard workups.
Observed Findings
- Positive complement split products (C3a, C4a, C5a) detected 2 years after acute EBV illness
- Complement activation markers remained elevated for 14 months of monitoring
- All conventional aetiological and immunological tests were negative or normal
- Patient clinical recovery coincided with normalization of complement measurements
- Post-viral onset clearly documented with well-established acute mononucleosis episode
Inferred Conclusions
- Complement system activation may represent a measurable abnormality in patients with post-viral ME/CFS despite normal conventional immune testing
- Complement activation markers may be a useful diagnostic tool or disease activity monitor in ME/CFS
- The association between complement activation and clinical recovery suggests immune dysregulation may be central to disease persistence
Remaining Questions
- How frequently is complement activation present across the broader ME/CFS population?
- Does complement activation predict disease duration or recovery in post-viral ME/CFS?
- Is complement-targeted therapy a viable treatment approach for ME/CFS patients with elevated complement markers?
What This Study Does Not Prove
This case report does not prove that complement activation causes ME/CFS, only that it was present in one patient. It does not establish how common this finding is across ME/CFS populations, whether complement activation is specific to post-viral cases, or what role it plays in disease pathogenesis versus being a secondary phenomenon.
Tags
Symptom:Fatigue
Biomarker:Blood Biomarker
Phenotype:Infection-Triggered
Method Flag:PEM Not DefinedWeak Case DefinitionNo ControlsSmall SampleExploratory Only
Metadata
- DOI
- 10.1136/bcr.08.2008.0819
- PMID
- 21686614
- Review status
- Editor reviewed
- Evidence level
- Early hypothesis, preprint, editorial, or weak support
- Last updated
- 12 April 2026
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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